The frequency of rape of civilians and other forms of sexual violence varies dramatically across conflicts, armed groups within conflict, and units within armed groups. The literature generally neglects these contrasts, focusing on cases of widespread rape. Yet rape is not inevitable during war. Many armed groups, including some state militaries, insurgent groups, and ethnic groups, do not engage in widespread rape despite frequent interaction with civilians. Some armed groups engage in ethnic cleansing the classic setting for widespread rape without engaging in sexual violence. After developing a theoretical framework emphasizing the strategic choices on the part of armed group leadership, the norms of combatants, dynamics within small units, and the effectiveness of military discipline, the discussion will focus on how policy-makers might leverage such variation towards more effective policies against wartime sexual violence.